U.N. forces have deployed ground troops, attack helicopters and drones to support a campaign by Democratic Republic of Congo's army against rebels in the northeast of the country, the head of its U.N. peacekeeping mission said on Wednesday.

The offensive against the Ituri Patriotic Resistance Force (FRPI) marks the first time the peacekeepers have provided major combat support to Congo's army since a row in January over the command of a separate operation against Rwandan Hutu rebels.

In that operation, the U.N. mission refused to work with two Congolese generals accused of human rights violations, leading the government to break off most military cooperation.

The U.N. Congo mission is the world's largest and it has gone into action in the country's eastern provinces to combat armed groups, dozens of which plague the region.

The offensive against the FRPI in Oriental Province is the most important since a successful joint campaign against the Rwandan-backed M23 rebellion in 2013, said mission head Martin Kobler.

"Here you have the proof that if we are truly united with the [Congolese army], if we can support [their] operations, it's worth it and produces results," Kobler told a news conference.

In the first detailed account of the offensive that began last week, Kobler said the army intervened to prevent rebels from marching on the town of Gety after surrender talks with the FRPI broke down in the nearby town of Aveba.

Combat continued this week but the FRPI's estimated 400 fighters have been dispersed into small groups, Kobler's deputy, David Gressly, told Reuters on Monday, adding he had no reports of civilian casualties.

The FRPI, first formed in 2002, is regarded as one of the most rapacious rebel groups in the east, exploiting reserves of gold, diamonds and timber.

Kobler said more talks are needed with the government before the United Nations can resume supporting joint operations against the Rwandan rebels, the Democratic Forces for the Liberation of Rwanda, whom Congo is fighting unilaterally.